Linear and Nonlinear Laser Spectroscopy of Surface Adsorbates with Sub-Monolayer Sensitivity

An experimental setup consisting of three highly sensitive spectroscopic methods for the investigation of the optical properties of surface adsorbates at low coverages is presented. The three spectroscopies cover a large wavelength range from ultraviolet to infrared and can be applied from ambient conditions down to ultrahigh vacuum. For the IR and the visible range, surface-sensitive cavity ringdown spectroscopy is used; the UV region is covered by surface second harmonic generation spectroscopy, a nonlinear technique. The potential of the setup is revealed by measurements of the laser dye Rhodamine 110 that is spin coated on a substrate. The reliability of the methods is verified by comparing obtained spectra with those obtained using standard techniques. Finally, the sensitivity of all three methods is estimated and shown to be sensitive enough to perform measurements in the sub-monolayer limit (in the best case down to